The present disclosure relates generally to subterranean drilling operations and, more particularly, to directional drilling operations and tools therefor.
Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation are complex. Typically, subterranean operations involve a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.
A wellbore may be drilled using a drill bit attached to the end of a generally hollow, tubular drill string extending from an associated well surface. Rotation of the drill bit progressively cuts away adjacent portions of a downhole formation using cutting elements and cutting structures disposed on exterior portions of the drill bit. After the wellbore is drilled, a subsequent casing operation may be performed to install metal casing along selected portions of the wellbore and cement the casing in place. In other methods, so-called casing drilling may instead be employed, wherein the casing string itself is used as the drill string during drilling. This can be accomplished, e.g., by imparting rotation to the casing, which is operatively coupled to the drill bit so as to impart rotation to the bit, as well.
In some instances, cased drilling can instead or in addition be carried out through use of a down-hole mud-motor or positive displacement motor (PDM), which may be part of a bottom hole assembly (BHA) located on the drill string proximate to a downhole end of the drill string. Such a motor may be coupled (e.g., latched) to the casing string proximate to a bottom end of the casing string, and further operatively coupled to the drill bit. The motor may be actuated (e.g., by mud flow through the motor) so as to impart rotation on the drill bit, without requiring rotation of the casing string. Cased drilling may eliminate the need to remove the drill string (sometimes referred to as “tripping” or “tripping out” the drill string) in order to insert casing into the borehole (sometimes referred to as “running pipe”); the casing is already inserted into the borehole as drilling progresses.
A BHA in cased or non-cased drilling may include a device or devices for implementing directional drilling, that is, the steering of the drill bit. Steering the drilling assembly may be useful for various reasons, such as to avoid particular formations or to intersect formations of interest. Steering the drilling assembly includes changing the direction in which the drilling assembly/drill bit is pointed. An example of a directional drilling device is a Rotary Steerable System (RSS), which may cause axial deviation of the drill bit in various ways, such as “point-the-bit” or “push-the-bit.” In a typical “point-the-bit” system, changing the direction in which the drilling assembly/drill bit is pointed includes exerting a force on a flexible drive shaft connected to a drill bit. In a typical “push-the-bit” system, changing the direction in which the drilling assembly/drill bit is pointed includes exerting a force on the borehole wall.
Steering the bit can result in drilling a deviated borehole from a straight section of the wellbore. In a simplified application, the wellbore is a straight vertical hole, and a drilling operator desires to drill a deviated borehole off the straight wellbore, e.g., in order to thereafter drill substantially horizontally in an oil- or gas-bearing formation, or other subterranean formation. The deviation need not necessarily result in horizontal drilling, of course, as other degrees of deviation from a vertical wellbore may be employed in directional drilling.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.